Definitely go to CAB. A lot of people in your situation feel scared of bankruptcy but it can often be their salvation & lifts a great weight off the shoulders when it takes place.
From what you say I very much doubt whether an IVA would be appropriate - it would need a substantial amount of spare cash for you to pay each month for 5 years, & would not cover the secured debts.
If you decide on bankruptcy you could stop paying the mortgage to raise the fee & to raise money for a deposit & initial rent on somewhere to live. The house would be repossessed & sold and all the secured debt would be included in the bankruptcy. If you had to pay anything at all it would be only for a period of 3 years. Go to Insolvency Service website & download their various booklets to find out more.
Your relations with your brother will be unlikely to improve whatever you do, as you just don't have the money to pay him back. He would be a creditor in any bankruptcy and you would have to treat him exactly the same as any other creditors - you must not give him any preference. However, what you do after you get discharged from bankruptcy is entirely between the 2 of you.